German Patent Application No. 96 44 164 describes a dielectric element which is located in the beam path of the radar system and possesses at least one arrangement made up of electrically conductive traces. The arrangement is to be dimensioned and/or arranged such that its effect on the beam path of the electromagnetic waves is negligible. This is achieved by the fact that the arrangement has conductive traces whose width is no more than .lambda./10 and whose spacings from one another are at least .lambda./4, .lambda. denoting the free-space wavelength of the electromagnetic waves being used. The conductive traces themselves should extend largely perpendicular to the polarization plane of the radiated or received waves.
Also described is the possibility of dividing the electrically conductive arrangement into at least two portions separated from one another, so that the electrical resistance and capacitance between the two separate portions can be measured. These two variables contribute to the so-called loss angle tan .delta. of the coating material, which allows conclusions to be drawn regarding the magnitude of any soiling or of a coating on the dielectric element.
Thick-film technology in the case of elements made of ceramic, and known printing methods in the case of plastic elements, are cited as possibilities for manufacturing the electrically conductive arrangement on the dielectric element.
Nothing is set forth in German Patent Application No. 1 96 44 164 regarding the manufacture of electrically conductive traces which run within a dielectric element.
German Patent Application No. 1 97 24 320 describes a heatable antenna lens made up of a dielectric element which possesses therein an arrangement of electrically conductive traces. The lens is configured such that the electrically conductive arrangement does not lie in one plane, and such that the electrically conductive arrangement is; arranged close to the convex external surface of the lens. Attachment of the heating contacts is accomplished through holes in the lens base element. The material indicated for the lens is preferably a thermoplastic such as polycarbonate or polyethylene.
A two-stage injection process is set forth for manufacture of the lens. In this, a lens base element with a groove preferably of continuously meandering shape is first injection-molded. A resistance wire is placed into this continuous groove. This intermediate assembly is then injection-coated with a surface layer, preferably made of the same material as the lens.
A disadvantage of German Patent Application No. 197 24 320 is that the electrically conductive traces that are laid in place can slip during the second injection-molding operation. If the intended position of the electrically conductive traces were to change under the injection-molding pressure, subsequent overheating and damage to the plastic, and possibly to the wire, at those points would be possible.